Case shift mechanism



Jan. 23, 1962 E. G. HOFFMAN CASE SHIFT MECHANISM 2 Sheets-Sheet 1 Filed Nov. 25, 1960 INVENTOR ERNEST G. HOFFMAN] 7 2M ATTORNEYS Jan. 23, 1962 E. G. HOFFMAN 3,0179979 CASE SHIFT MECHANISM Filed Nov. 25, 1960 2 Sheets-Sheet 2 INVENTOR ERNEST G. HOFFMAN ATTbRN EYS 3,@l7,979 Patented Jan. 23, 1962 3,017,979 CASE SHUT MECHANISM Ernest G. Hoffman, Storrs, Conn, assignor to Royal McBee (Iorporation, Port Chester, Nfltl, a corporation of New York Filed Nov. 25, 1960, Ser. No. 71,529 8 Claims. (Cl. 197-74) This invention relates to an improved power operated case shift mechanism for typewriters and the like, and more particularly relates to a novel power drive arrangement comprising a plurality of roll cams which alternately cooperate with a driven power roll so as to displace the type bar supporting segment of an electric typewriter to upper and lower case positions respectively.

One object of the instant invention is to provide a reliable, efiicient, and inexpensive case shift mechanism having only a relatively few simple parts.

Another object of the invention is to provide a novel case shift apparatus for electric typewriters wherein a pair of roll cams are mounted on an actuating crank means and are alternately swung into operative engagement with a rotating power roll.

A further object of the invention is to provide a novel case shift mechanism for an electric typewriter wherein an actuating crank means carrying a pair of roll cams is biased by an overcenter spring so as to be capable of alternately swinging said roll cams into operative engagement with a power roll so that the typewriter segment is alternately displaced in two directions.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein:

FIGURE 1 is an exploded perspective view illustrating the principle parts of the instant apparatus.

FIGURES 2, 3 and 4 are active side elevational views of the various parts of the apparatus shown in FIGURE 1.

Unless otherwise indicated it is to be assumed that the various elements described are suitably supported on the machine frame in any conventional manner.

To a main rotatably supported cross shaft there is fastened a pair of laterally spaced segment operating arms 11 and 12. The forward ends 13 and 14 of these two arms are interconnected by a shaft 15 which is articulately connected at its ends to either side of a type bar supporting segment 16 by means of links 17 and 13 respectively. The segment 16 is conventionally mounted and supported for the usual vertical case shift movement, the upper and lower limits of which are respectively determined by the engagement of the said operating arms with the upper and lower adjustable stops 2% and 21 secured to the machine side frames. The shaft 15 is biased to an upper and lower position by means of a pair of main overcenter springs 22 and 23 which are respectively anchored on stud shafts 24 and 25 fixed to the machine frame; segment 16 thus being yieldably retained in either its upper or lower case position.

Rotatably mounted on the center portion of said cross shaft ill is an actuating bell crank 26 which is yieldably biased in either rotative direction by means of an overcenter spring 27 that is anchored on a cross shaft 28. The forwardly extending leg 31} of the bell crank is formed with a vertical slot 31 through which the said shaft 15 extends, thereby permitting a limited amount of swinging movement of the bell crank 26 relative to the shaft 15. As will be apparent, displacement of the bell crank beyond the limits effectively defined by the ends of slot 31 will serve to vertically shift the shaft 15 together with the segment operating arms 11 and 12 and the Segment 16. A pair of roll cams 32 and 33 are rotatably mounted on the bell crank by means of studs 36 and 37 and have roughened eccentric peripheral surfaces 46 and 41 respectively. An elongated spring 42 is anchored at either end on the roll cam pivot studs 34 and. 35 and passes obliquely about the studs 36 and 37 and around the peripherally grooved hub portion 43 of the bell crank 26. Spring 42 yieldably urges the roll earns 32 and 33 into normal engagement with studs 44- and 435 respectively fixed to said bell crank. The roll cams are adapted to alternately swing into frictional engagement with a power roll 56 which is rotatably mounted and continuously driven in the usual manner and which is provided with the usual type rubber coating 47.

Bell crank detent control means are provided for respectively preventing and permitting swinging movement of the bell crank and the roll cams under the action of the overcenter spring 27; such means including a detent control lever 50 which is fastened to the center portion of the rotatably mounted cross shaft 51. The forward end of lever 50 is formed with a bent off car 52 which is adapted to cooperate with the two opposed and vertically offset shoulders 53 and 54 formed on the upper end of the leg 55 of bell crank 26. To the outer end of the shaft 51 there is fastened an arm 56 which is articulately connected to the usual shift key lever 57 by means of a link 66. Movement of the key lever 57 will serve to swing said detent lever 50 between its upper and lower detenting positions. A similar operating linkage is provided for the other end of the cross shaft 51 thereby permitting actuation of the lever Stl by depression of either of the two usual shift keys of the typewriter.

The normal condition of the various parts is illustrated in FIGURE 1. Here the main overcenter springs 22 and 23 maintain the arms 11 and 12 in engagement with the upper adjustable stops 20 so that the shaft 15, links 17 and 18 and segment 16 are normally retained in their elevated or lower case positions. The overcenter spring 27 urges the actuating bell crank 26 in a clockwise direction to a normal position determined by engagement of the bell crank shoulder 53 with the bent off car 52 of control lever 511. Under these conditions the cross shaft 15 is disposed near the center of the said bell crank slot 31. When either of the case shift keys is depressed the bent off car 52 of the detent lever will be elevated to a position just above shoulder 53 thus freeing the bell crank 26 for a slight clockwise displacement under the. action of overcenter spring 27 as permitted by said slot 31. The roll cam 32 is thus swung into operative engagement with the periphery of the rotating power roll 46, as shown in FIG- URE 2, whereupon the resultant roll cam rotation will serve to power drive the bell crank through a counter clockwise stroke in a well known manner. During this power stroke the upper end of the slot 31 will engage the cross shaft 15 and hence will impart a counter clockwise shift movement to the segment operating arms 11 and 12. At the end of the power stroke the segment 16 together with the forward ends 13 and 14 of arms 11 and 12 will have been moved to their lowered or upper case positions and will be held there by the action of the main overcenter springs as illustrated in FIGURE 3.. The displaced bell crank 26 will now be biased in a counter clockwise direction by the overcenter spring 27 so that the bell crank shoulder 54 engages the now elevated bent off car 52 as illustrated in FIGURE 4. In this condition of the parts the roll cam 32 will have been spring restored to its normal rotative position and the cross shaft 15 will again be disposed near the middle of the bell crank slot 31.

As long as the case shift key is held depressed the segment 16 will remain in the lowered or upper case position. When the shift key is permitted to move to its normal elevated position the bent ofi ear 52 of detent lever 50 will be lowered thereby allowing the bell crank 26 to swing in a counter clockwise direction under the action of the overcenter spring 27 as permitted by the slot 31 and the undercut portion 61 of the bell crank. This action will swing the roll cam 33 into operative engagement with the power roll 45 so that the bell crank is thereafter power driven through a clockwise stroke in a manner similar to that of the previous power stroke. During this stroke the bottom of slot 31 Will engage and elevate the cross shaft so that all the parts are restored to their normal positions as illustrated in FIGURE 1. The segment 16 will remain in its elevated or lower case position until one of the case shift keys is again depressed.

As may be readily seen the overcenter spring 27 changes its direction of rotational bias on the bell crank 26 each time the latter partakes of a power stroke. Releasing this biasing action by operation of the detent lever 50 serves to engage the proper roll cam with the power roll to cause a reversal in the direction of segment shift movement from that of the next previous shift movement. As will be apparent the instant drive action may be utilized to power operate other elements of the machine.

While there is in this application specifically described one form which the invention may assume in practice, it will be understood that this form of the same is shown for purposes of illustration only and that the invention may be modified and embodied in various other forms without departing fro-m its spirit or the scope of the appended claims.

The invention claimed is:

1. In an electric typewriter having a printing element support member mounted for case shifting movement, and a rotatably driven power roll; the improvement comprising operating means for shifting said member, crank means connected to said operating means, a pair of roll cams operatively mounted on said crank means and adapted to be alternately biased into operative frictional engagement with said power roll so as to thereby power shift said member, and a key controlled lever for controlling the movement of said roll cams into engagement with said power roll.

2. In an electric typewriter having a printing element supporting member arranged for case shifting movement, and a rotatably driven power roll; the improvement comprising a crank member operatively connected to shift said member, a pair of roll cams movably mounted on said crank member and adapted to be alternately moved into frictional engagement with the opposite sides of said power roll so as to power operate said crank means, and control member for permitting and preventing the alternate engagement of said roll cams with said power roll.

3. In a typewriter having a printing element supporting member mounted for case shift movement; and a rotatably driven power roll: the improvement comprising operating means connected to said member; means for actuating said operating means including crank means, and a pair of roll cams rotatably mounted on said crank means and adapted to alternately engage the periphery of said rotatably driven power roll so as to power actuate said operating means; and a control lever mounted for engagement with said crank means so as to permit and prevent the alternate engagement of said roll cams with said power roll.

4. Apparatus as defined by claim 3 wherein said crank means is yieldably biased by an overcenter spring and said control lever permits and prevents the biasing action of said spring in controlling the said alternate engagement of said roll cams with said power roll.

5. In an electric typewriter having a segment mounted for shifting movement to upper and lower case positions, and a continuously driven power roll rotatably mounted in the machine frame, the improvement comprising an operating linkage for moving said segment, crank means movably mounted on the machine frame and connected to said operating linkage, a pair of roll cams rotatably mounted on said crank means, said crank means being movable to alternately displace said roll cams into operative frictional engagement with said power roll, and a key controlled lever mounted on the machine frame for controlling that movement of said crank means which permits said roll cams to move into alternate engagement with said power roll.

6. Apparatus as defined by claim 5; additionally comprising means for yieldably retaining said segment in its said upper and lower positions respectively, and means for yieldably biasing said crank means in either of two directions.

7. In an electric typewriter having a segment mounted for shifting movement to upper or lower case positions respectively, and a continuously driven power roll rotatably mounted in the machine frame; the improvement comprising an operating linkage for moving said segment, means for alternately yieldably biasing said operating linkage in either one of two effective directions of movement, crank means pivotally mounted on the machine frame and operatively connected to said operating linkage so that there is a predetermined amount of relative movement permissible between said crank means and said operating linkage, means for alternately yieldably biasing said crank means in either rotative direction, a pair of roll cams mounted on said crank means so as to be alternately engageable with the periphery of said power roll and thereby power drive said segment to its upper and lower positions respectively, and key controlled means for permitting and preventing said relative movement thus controlling the movement of said roll cams into alternate engagement with said power roll under the action of said yieldable biasing means for said crank means.

8. A drive mechanism for a machine member which is to be alternately displaced to two different positions; comprising operating linkage for moving said member, means for alternately yieldably biasing said operating linkage in either one of two effective directions of movement, crank means movably mounted on the machine frame and operatively connected to said operating linkage so that there is a predetermined amount of relative movement permissible between said crank means and said operating means, means for alternately yieldably biasing said crank means in either of two elfective directions of movement, a pair of roll cams mounted on said crank means so as to be alternately engageable with the periphery of said power roll and to thereby power drive said member to its first and second positions respectively, and control means for permitting and preventing said relative movement thus controlling the movement of said roll cams into alternate engagement with said power roll under the action of said yieldable biasing means for said crank means.

References Cited in the file of this patent UNITED STATES PATENTS 

